This invention relates to traffic control expansion and testing systems. More specifically, this invention relates to extending the service life of “aging” fixed-size traffic-control cabinets, within at least one traffic-control network. In addition, this invention relates to providing a system for efficient testing of NEMA-standard TS-1, TS-2, 170, and 2070 detector cards.
Current traffic control systems frequently utilize local electronic detectors that output a signal in the presence of a vehicle or preemption. These systems are often used to adjust signal sequences and timing, collect traffic data, activate special control devices, measure speeds, etc. The National Electrical Manufacturers Association (NEMA) has established standards for electronic vehicular traffic controller assemblies. These standards have been adopted by many traffic control equipment manufacturers along with a majority of governing agencies having jurisdiction over the traffic control systems based on such products.
Controllers/detectors based on the NEMA traffic control system standards provide a basic set of features and standard connectors. The detectors are generally described by the following attributes:                a) They are rack or shelf mounted;        b) They may comprise a pluggable, interchangeable bus interface unit to convert high-speed serial data to a format required by individual detectors or contact closures;        c) They may provide communications with controller unit, as described above;        d) They provide per-channel diagnostic data (open loop, shorted loop, excessive inductance change, watchdog failure, etc.);        e) They provide detector reset capability; and        f) They operate from either 12-volt direct current (DC) or 24-volt DC power supply.        
The standardization of NEMA-compliant traffic control cabinets has produced an unexpected problem for jurisdictions maintaining a plurality of older fixed-size traffic-control cabinets. Many of the existing NEMA-compliant traffic control cabinets were supplied from the factory pre-equipped to support a fixed number of rack or shelf mounted traffic-signal components. Many older existing traffic-control cabinets are now at full hardware capacity, incapable of receiving additional hardware without significant and costly rework or replacement. This often forces the overseeing jurisdiction to choose between omitting new, possibly mandated, technology upgrades, or committing to the costly reworking or replacement of the older “aging” cabinets. A need thus exists for systems and methods for extending the service life of such “aging” fixed-size traffic-control cabinets by facilitating the adding of additional required function within the cabinets, without major rework or replacement of the cabinets or internal components.
Like any electronic system, NEMA controller/detector apparatus require periodic maintenance and testing. Testing is often done in the field by accessing the devices typically located within the local traffic-control cabinet. Field testing is often hindered by adverse environmental conditions, which may include adverse weather conditions, extreme hot/cold temperatures, traffic, noxious fumes, excessive noise levels, etc. Removing and transporting the devices to a remote testing site greatly increases the overall cost of service. Clearly a need exists for more efficient means for providing such field maintenance and testing. A system allowing both hardware expansion within a traffic cabinet and a means for convenient in-the-field testing would be of great benefit to the traffic-control field.